1. Field of the Invention
This invention relates to an expandable data processing system and more particularly to an expandable processing chassis having a modular backplane for distributing high-speed signals.
2. Description of the Related Art
In conventional data processing and communications systems, circuit boards or circuit board "modules" are housed in a circuit housing such as a "card cage" or a circuit board "shelf." Each circuit housing is generally capable of housing multiple circuit boards which are coupled by a common backplane. A backplane is a planar circuit, designed to electrically couple circuit boards which are mounted perpendicular to the backplane. A data processing system can be built using a circuit housing containing multiple circuit boards interconnected by a single backplane.
As a user's processing requirements increase, it is generally most cost effective to expand an existing data processing system rather than to install an entirely new system. Therefore, expandability is a desirable feature of a data processing system. Data processing systems are commonly expanded by incorporating additional circuit board housings into a processing system. In such systems, each circuit housing has a dedicated backplane which interconnects the circuit boards contained in each housing. Conventionally, the backplanes of multiple circuit housings are interconnected using cables or electrical connectors. Such interconnection, however, introduces undesired signal degradation, when processing high frequency signals. Impedance mismatch between the cable and the backplane and impedance discontinuities at the connectors introduce undesired transmission-line effects in high-speed systems. Thus, there is a need for an expandable high-speed processing system which does not generate undesired transmission-line effects.